1. Field of the Invention
The present invention relates to a substrate heating apparatus, a substrate heating method, a semiconductor integrated circuit device, a photomask and a liquid-crystal device.
2. Description of the Related Art
As a heating method of a conventional substrate heating apparatus, an oven-type heating method or a hot-plate-type heating method is employed. A substrate heating apparatus having an oven-type heating method of these methods is designed to indirectly heat a workpiece to be heated, for example, a substrate in a heating atmosphere inside a heat insulation chamber which serves also to shield heat on the precondition that a plurality of substrates are heated at a time.
On the other hand, in recent years, a substrate heating apparatus employing a hot-plate-type heating method has been generally used due to the necessity of forming what is commonly called xe2x80x9cinline processingxe2x80x9d with other apparatuses for the purpose of reducing the adhesion of particles onto a substrate and without human intervention.
An example of a conventional substrate heating apparatus employing a hot-plate-type heating method will now be described with reference to the schematic view of FIG. 1.
As shown in FIG. 1, a substrate heating apparatus 101 basically comprises a heater 111 and a heater block 112 formed on the heater 111.
In order to heat a substrate 121 by using the substrate heating apparatus 101, the substrate 121 is placed on the heater block 112 and the heater block 112 is heated by the heater 111 so as to heat the substrate 121 from the rear surface of the substrate 121. Therefore, the substrate 121 is heated via the heater block 112 by the heater 111.
In recent years, resist materials have been improved in order to form patterns finer than those of the known art. For example, a resist material utilizing a catalytic reaction during heating time has been developed, and such a resist material has been used in a semiconductor device manufacturing process. In such resist materials, acid generated in a resist material due to irradiation of light or irradiation of a charged particle beam reacts with a functional group having a high reactivity to acid due to heating after the irradiation, and the solubility characteristic of the resist material with respect to the developing solution varies, thus forming a pattern. The above-mentioned resist is generally called a chemical amplification-type resist.
However, use of a chemical amplification-type resist causes temperature conditions for heating after exposure or after the charged particle beam is irradiated to affect the reaction speed. For example, as shown in the relation view of FIG. 14 between the line width variation amount of a pattern and heating temperature, it can be seen that the temperature conditions during the heating period cause the line width of the pattern to vary. Therefore, presence of a temperature distribution on the surface of the substrate brings about undesirable results in high-precision pattern formation.
In a conventional oven-type substrate heating apparatus, since the heating chamber is opened and closed when a heating process is started, the reproducibility of temperature and the controllability of the temperature inside the heating chamber are low. Also, since the substrate is indirectly heated, the temperature distribution under the substrate surface is considerably unfavorable. Further, also in the conventional substrate heating apparatus employing a hot-plate-type type heating method, the temperature distribution of the substrate surface is unfavorable. For these reasons, it is not possible to form high-precision patterns.
An example of the above will be described below with reference to FIG. 15. In FIG. 15, the vertical axis shows differences from the reference dimension (line width=1.0 xcexcm) of the pattern, i.e., dimensional variations of the pattern, and the horizontal axis shows measurement positions with respect to the effective area (a 110 mm square) in a photomask.
The patterns measured in the example are formed by the processes described below. That is, an acid catalytic reaction-type resist is coated on a glass substrate having a thickness of 6 mm and heated to remove a resist solvent. Then, the resist film is irradiated with an electron beam, after which the glass substrate is heated by the substrate heating apparatus of a hot-plate-type heating method. Then, a development process is performed to form a pattern.
The dimensional variations of the resist pattern in this case were 3"sgr"=0.045 xcexcm.
It can be seen in FIG. 15 that (a) the dimensional variation varies from a positive variation to a negative variation toward a particular direction (the front side in the drawing in this example). That is, since heating is performed only from the rear surface of the glass substrate in the substrate heating apparatus of a hot-plate-type heating method, the pattern dimension distribution depends upon the parallel relation between the heater block and the substrate. For this reason, when the parallel relation is poor, variations in pattern dimensions having directivity occur.
Also, (b) a large variation of the pattern dimension occurs near the outer peripheral portion of the substrate. This is caused by the heat loss which occurs due to the convection of air.
Such phenomena as the above-described (a) and (b) appear conspicuously in cases where thermal conductivity is as low as in a glass substrate and the thermal capacity increases with the thickness of the substrate. In particular, in the manufacture of photomasks, it is practically impossible to obtain patterns having high dimensional precision.
Further, (d) also in a silicon substrate having relatively high thermal conductivity, problems similar to those described above have been reported [47th Symposium On Semiconductor Integrated-Circuits, Proceeding Papers (1994), Yamamoto et al., P60], presenting a considerable problem in a manufacturing process.
The present invention has been achieved to solve the above-described problems. It is an object of the present invention to provide a substrate heating apparatus and a substrate heating method which excel in achieving uniformity of pattern dimension and which excel in reducing dimensional variations in the portion under the substrate surface, and to provide a semiconductor integrated circuit device, a photomask, and a liquid-crystal display device, in each of which each substrate is heated by the substrate heating apparatus.
To achieve the above-described objects, according to the present invention there is provided a substrate heating apparatus, a substrate heating method, a semiconductor integrated circuit device, a photomask and a liquid-crystal device.
More specifically, the substrate heating apparatus used in a manufacturing process for semiconductor devices, heats a substrate before or after irradiation of light for forming a pattern by using a photosensitive material formed on a substrate, or before or after irradiation of a charged particle beam for forming a pattern by using a material that is sensitive to charge particles, formed on a substrate. The substrate heating apparatus comprises a first heater which is a heat source for heating a substrate from the obverse surface thereof and a second heater which is a heat source for heating the substrate from the rear surface thereof, wherein the temperatures of the first and second heaters can be set individually.
The surface of the first heater on the substrate must be spaced from the surface of this substrate, and the space is set to be 10 mm or smaller. It is preferable that a recessed portion be formed on at least a part of the surface of the first heater on the substrate side. Further, the second heater comprises a third heater which constitutes the central portion of the second heater and the area adjacent to the central portion of the second heater, and a fourth heater disposed around the side peripheral portion of the third heater.
In the substrate heating apparatus, the first heater which heats a substrate from the obverse surface thereof and the second heater which heats the substrate from the rear surface thereof are provided; therefore, it becomes possible to heat the substrate from both sides. Therefore, heat loss on the surface of the substrate is suppressed, and the surface temperature of the substrate reaches a stable temperature at an early stage.
Further, since the temperatures of the first and second heaters can be set individually, it becomes possible to set the surface temperature of the substrate at any desired value.
Further, since a recessed portion is formed in at least a part of the surface of the first heater on the substrate side, it is possible to obtain uniform heat radiation on the surface of the substrate. Therefore, the surface of the substrate is uniformly heated.
Further, since the second heater comprises a third heater which constitutes the central portion of the second heater and the area adjacent to the central portion of the second heater, and a fourth heater disposed around the side peripheral portion of the third heater, heating from the rear surface of the substrate is controlled so that the temperature of the surface of the substrate becomes uniform when the substrate is heated to an increased temperature.
The substrate heating method comprises the step of heating a substrate before or after irradiation of light for forming a pattern by using a photosensitive material formed on the substrate, or before or after irradiation of a charged particle beam for forming a pattern by using a material that is sensitive to charge particles, formed on the substrate, wherein the substrate is heated at a temperature T1 from the obverse surface thereof and heated at a temperature T2 from the rear surface thereof into a temperature state independently of the heating from the obverse surface of the substrate. The temperatures T1 and T2 should preferably satisfy the relation of 0.7xe2x89xa6T1/T2xe2x89xa61.6.
In the above-described substrate heating method, since the substrate is heated at a temperature T2 from the rear surface thereof and the substrate is heated at a temperature T1 from the obverse surface to a temperature state independent of the heating from the rear surface of the substrate, heat loss on the surface of the substrate is suppressed, and the surface temperature of the substrate reaches a stable temperature at an early stage. Further, the surface temperature of the substrate reaches a desired temperature, and a desired temperature distribution is formed by appropriately setting the ratio of temperature T1 to temperature T2.
Further, since the temperatures T1 and T2 are set so as to satisfy the relation of 0.7xe2x89xa6T1/T2xe2x89xa61.6, dimensional variations in the pattern are reduced to less than conventional dimensional variations in a pattern because the surface of the substrate is heated uniformly.
When the temperatures are set to T1/T2 less than 0.7, since the temperature T1 on the obverse surface of the substrate becomes much lower than the temperature T2 on the rear surface of the substrate, the effect of suppressing heat loss from the surface of the substrate tends to decrease. Also, when the temperatures are set to 1.6 less than T1/T2, the temperature T2 on the rear surface of the substrate becomes very low and it becomes difficult to obtain a stable substrate surface temperature distribution for a substrate having a large thermal capacity.
The semiconductor integrated-circuit device is formed by heating a substrate in a lithographic process conducted in the manufacture of semiconductor integrated-circuit devices by using a substrate heating apparatus which comprises a first heater for heating a substrate from the obverse surface thereof, from which a semiconductor integrated-circuit device is formed, and a second heater for heating the substrate from the rear surface thereof and which is capable of individually setting the temperatures of the first and second heaters.
In the semiconductor integrated-circuit device, since the substrate is heated in a lithographic process in the manufacture of semiconductor integrated-circuit devices using a substrate heating apparatus which heats a substrate from above and below, the portion under the surface of the substrate is heated almost uniformly, and therefore, dimensional variations in the pattern are reduced. Therefore, since a high-precision pattern can be formed, variations in the electrical characteristics due to dimensional variations in the pattern are reduced.
The photomask is formed by heating a substrate in a lithographic process conducted in the manufacture of photomasks by using a substrate heating apparatus which comprises a first heater for heating a substrate which constitutes a photomask from the obverse surface thereof and a second heater for heating the substrate from the rear surface thereof and which is capable of individually setting the temperatures of the first and second heaters.
In the photomask, since the substrate is heated in a lithographic process in the manufacture of photomasks by using a substrate heating apparatus for heating a substrate which constitutes the photomask from both sides thereof, the portion under the surface of the substrate is heated almost uniformly. Therefore, dimensional variations in the pattern can be reduced.
The liquid-crystal display device is formed by heating a substrate in a lithographic process conducted in the manufacture of liquid-crystal display devices by using a substrate heating apparatus which comprises a first heater for heating a substrate which constitutes a liquid-crystal display device from the obverse surface thereof and a second heater for heating the substrate from the rear surface thereof and which is capable of individually setting the temperatures of the first and second heaters.
In the liquid-crystal display device, since a substrate is heated in a lithographic process in the manufacture of liquid-crystal display devices by using a substrate heating apparatus for heating a substrate which constitutes a liquid-crystal display device from both sides of the substrate, the portion under the surface of the substrate is heated almost uniformly and therefore, dimensional variations in the pattern are reduced. Therefore, since a high-precision pattern can be formed, variations in the electrical characteristics due to dimensional variations in the pattern are reduced.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.